The present invention relates to the general field of low-pressure turbines of aviation turbomachines. It relates more particularly to a particular way of assembling the rotor of the low-pressure turbine on the low-pressure shaft in order to facilitate assembly and disassembly.
An aviation turbomachine is typically provided with a high-pressure turbine placed at the outlet from a combustion chamber. A low-pressure turbine is disposed downstream from the high-pressure turbine in the flow direction of the gas coming from the combustion chamber. An exhaust case for the gas flow is assembled downstream from the low-pressure turbine. Thus, the gas coming from the combustion chamber passes through the high-pressure and low-pressure turbines in order to drive them in rotation, and is then exhausted via the exhaust casing.
The low-pressure turbine of the turbomachine essentially comprises a rotor (blades and disks) mounted on a low-pressure trunnion. The trunnion is assembled on a low-pressure shaft of the turbomachine via a fluting system that enables the low-pressure shaft to be driven in rotation. Similarly, the high-pressure turbine comprises a rotor (blades and disks) mounted on a high-pressure trunnion. A rolling bearing placed on the low-pressure trunnion enables the high-pressure trunnion to be supported to rotate relative to the low-pressure shaft.
FIG. 2 shows part of a prior art assembly of a low-pressure turbine rotor on the low-pressure shaft of a turbomachine. In this figure the rotor 100 of the low-pressure turbine 102 is fixed on a low-pressure trunnion 104. This low-pressure trunnion 104 extends axially firstly in an upstream direction to a rotor 106 of the high-pressure turbine 108, and secondly downstream to an exhaust casing 110 of the turbomachine. The rotor 106 of the high-pressure turbine 108 is secured to a high-pressure trunnion 112 extending axially towards the low-pressure trunnion 114.
The low-pressure turbine 102 drives a low-pressure shaft 114 in rotation via fluting 116 provided at the upstream end of the low-pressure trunnion 104. A first rolling bearing 118 is mounted at the downstream end of the low-pressure trunnion 114 in order to guarantee support and centering of the low-pressure-turbine 102 relative to the exhaust casing 110 of the turbomachine. A second rolling bearing 120 is also mounted on the low-pressure trunnion 104 in order to support the high-pressure trunnion 112 in rotation. The second bearing is disposed between the first bearing 116 and the fluting 116. In addition, a sealing gasket 122 is mounted on the low-pressure trunnion 104 between the second bearing 120 and the fluting 116. Associated with a plate 124, this gasket provides sealing between an air enclosure 126a and an oil enclosure 126b. 
Such a low-pressure turbine assembly presents numerous drawbacks, in particular when disassembling the low-pressure turbine.
While a turbomachine is being disassembled (whether partially or completely), e.g. during maintenance, the various elements are typically removed through the rear of the turbomachine, i.e. in an upstream to downstream direction. Specifically, when the low-pressure turbine is to be disassembled, it is necessary in particular to begin by removing the exhaust casing. The high-pressure turbine (trunnion and rotor) is then subsequently withdrawn by being moved axially towards the downstream end of the turbomachine.
With the assembly shown in FIG. 2, once the exhaust casing 110 has been withdrawn, removing the low-pressure turbine 102 gives rise to problems. When the low-pressure turbine 104 is caused to slide axially downstream, the second bearing 120 and the sealing gasket 122 supported by the low-pressure trunnion disengage from the high-pressure trunnion 112.
Withdrawing the second rolling bearing 120 then leads to the low-pressure shaft 114 being off-center relative to the high-pressure trunnion 112 (and thus relative to the high-pressure turbine 108), such that the low-pressure shaft 114 is no longer held radially after the low-pressure turbine 102 has been removed. In addition, withdrawing the gasket 122 has the effect of breaking the seal between the air enclosure 126a and the oil enclosure 126b, such that oil spreads into the air enclosure, leading to a risk of an oil leak.